An electric contact of this type is available and is used, for example, in the automobile industry.
Such an electric contact includes a metallic substrate, which is normally made of a copper-based alloy such as CuSn4 bronze, CuNiSi or the like, on which a contact layer made of tin is situated. The contact layer may be a hot-tin-plated or electrolytically deposited layer which has a thickness of a few micrometers. An intermediary layer made of intermetallic compounds such as CuSn4, Cu5Sn6 is formed by diffusion on the boundary surface with the substrate when a tin contact layer is used. The intermediary layer is harder than the contact layer and may grow as a function of the temperature.
Tin or a tin alloy is characterized by high ductility and good electric conductivity. Tin alloys or tin layers, however, have the disadvantage that they tend to wear off due to their low hardness and the resulting low wear resistance upon frequent insertions or vibrations caused by the vehicle or the engine, which results in increased oxidation, known as friction corrosion. Friction wear and/or friction corrosion may in turn result in failure of an electric automobile component associated with the contact in question, in particular a sensor, a control unit, or the like.
In tin or tin alloy layers of this type it is furthermore disadvantageous that the insertion forces for many applications are excessively high, because these contact layers have a strong tendency toward adhesion and high plastic deformability.
Furthermore, a tin-based contact layer of an electric contact, known as thermotin, is known in industry, which is made entirely of intermetallic phases and is manufactured by artificial aging. However, it has been found that thermotin has limited applicability, which may be shown in particular on the basis of chemical and abrasion testing.
Furthermore, Au—Co alloys on a nickel layer, silver plating on a copper or nickel layer, or gold plating were previously often used as contact layers in electric contacts.
In particular, silver-based, but also tin surfaces or contact layers tend toward cold fusion due to adhesion and are characterized by high friction coefficients in self-mated pairs.
Even in silver or gold layers previously used in electric contacts, oxidative wear of the substrate or of an intermediary layer used as an adhesion layer, often made of copper or nickel, may occur in the event of friction wear or flaking of the layer.